Conventional axial rolling heads comprise three profile rollers arranged offset by 120.degree. which are rotatably supported within a bearing unit. The bearing unit is supported by a shank which is clamped into a machine tool. The rolling head is kept in the direction of rotation, however, can move axially. The rolling head is forced on the rotating workpiece, with the feed being made by the axially freely movable rolling head while milling the thread.
Upon completion of the thread milling it is necessary to disengage the profile rollers with the workpiece. It is known to arrange the profile rollers on eccentric shafts, the rotation of which results in a change of the distance between the profile rollers. It is also known to secure to the eccentric shafts small gear wheels meshing with a central gear wheel which is arranged on the shank in a fixed position and cannot rotate. A helical spring with the one end is secured to the bearing unit and with the other end it is secured to the shank. The helical spring is biased, with the profile rollers being, in the operating position. As soon as the feed has reached a preset value the workpiece abuts against a rod axially provided within the shank of the rolling head. As a result, the bearing unit and the shank are axially moved apart and thus a claw clutch is divided between said parts. Now the spring can displace the bearing, unit by a given angle by twisting. In this way, the gear wheels are caused to also roll on the central gear wheel and twist the eccentric shafts for displacing the profile rollers. Thereafter, the workpiece can be removed from the thread rolling head.
Before starting a new working cycle it is necessary to "lock" the rolling head again. This usually is done by hand. A so-called spring housing with the helical spring contained therein is turned in reverse direction by hand or by corresponding means. As the helical spring is axially extended during the described releasing procedure the shank and the bearing unit are caused to be tensioned. As soon as the moving back of the spring housing has reached a preset value the claw clutch mentioned before locks into place again and the thread rolling head is locked.
It is the object of the invention to provide an axial thread rolling head where the thread rolling head can be locked automatically.
The axial thread rolling head according to the invention comprises a drive, preferably an electrical motor, arranged on the shank and connected to the bearing unit by means of a second gear for relatively twisting the bearing unit into the first direction of rotation by a preset angle of rotation as soon as the shank and the bearing unit have reached the second axial relative position. With other words the motor provided on the shank twists the bearing unit into the locking position of the rolling head by means of a suitable gear, with the claw clutch, as already mentioned before, being locked automatically again.
It goes without saying that there also can be used a hydraulic, pneumatic or another drive, especially a so-called direct drive which does not need a gear.
If using an electrical motor it is certainly thinkable to feed it front outside as it is stationarily arranged on the shank being axially movable only. However, a battery supply is to be preferred. Correspondingly, according to an embodiment of the invention, the shank comprises means for receiving a battery.
According to another embodiment of the invention, there is arranged on the shank at least one sensor for receiving a contactlessly transmitted control signal for the driving motor. Preferably, the sensor is an infrared sensor. If the rolling head according to the invention is arranged within a N/C machine the control for the driving motor may be part of the program. For this purpose, the N/C machine can also receive a signal when the thread rolling head has been released and/or the workpiece has left the rolling head so as to be aide to start the locking procedure. It goes without saying that besides the sensor a control circuit is also to be associated to the motor which causes the motor to be turned on and off as a result of the transmitted signal. Turning off, however, may be easily performed by a limit switch which turns off the motor as soon as a given angle of rotation has been reached.
There may be used various ways to form the gear so as to displace the bearing unit by twisting. According to an embodiment of the invention, there is arranged on the motor shaft a small pinion meshing with a toothed segment of a rotatably supported switch ring which transfers a rotational movement to the bearing unit. For this purpose, the switch ring may comprise an engaging portion which cooperates with an engaging portion of the bearing unit.
According to another embodiment of the invention, the motor is arranged within an annular casing provided on the shank. If using a battery box, it, preferably, also is annularly arranged on the shank and, preferably, is provided adjacent to the annular motor casing.
According to a further embodiment of the invention, the bearing unit comprises a spring housing rotatably supported on the shank and forming the claw clutch together with the shank. It goes without saying that the relative rotation of the spring housing and the shaft is only possible if the claw clutch is out of mesh. The spring housing and the switch ring are surrounded by a common covering. The covering causes the switch ring to be also engaged in case of an axial displacement of the spring housing as a result of the before described abutment against the workpiece.
The invention will be more detailedly explained hereinafter with the aid of drawings.